A method for precontrolling and feedback controlling a variable is known, for example from the controlling of the lambda value. For the explanation of such a method, let it first be assumed that the airstream fed to an internal combustion engine is constant. A quantity of fuel is fed which should lead to the lambda value 1. The maintaining of this desired value is monitored by a lambda sensor. If, on account of a change in the value of a disturbance, a deviation of the lambda actual value from the lambda set value occurs, the quantity of fuel metered is changed such that the lambda value 1 is restored. Then it is assumed that not only the value of a disturbance changes, but that also the air flow changes. This also leads to a change in the lambda actual value and consequently to a system deviation, which is compensated again by the control method. However, this correcting costs time. In order to shorten the time of a response to a change in the air flow, it is known to measure the respective air flow in a calibration process and to determine the associated value of the quantity of fuel which leads to the lambda value 1 when the calibration conditions exist. If then, in actual operation, the conditions deviate from the calibration conditions, only these relatively small deviations remain to be corrected, but no longer the large changes which are caused by arbitrary changing of the air flow.
In order to determine the correct precontrolled variable, in the case of the example, the air flow has to be measured. If, on account of aging effects, the initial value of the measuring device changes over the course of time with the same air flow, that is the same input value, the precontrolled value is incorrectly determined. This error too can be compensated by means of the feedback control, but with the already-mentioned disadvantage of the slow response in comparison with the precontrol. However, adaptation processes have already been developed in order to take into account, for example, such aging effects in the precontrol. In the case of the known adaptation methods, however, only a single adaptation value or a single set of adaptation values is determined for the entire measuring range. This leads to the corrected precontrol only operating accurately in the measuring range for which the adaptation value coincides with the deviation caused by aging. In order to achieve higher accuracy over the entire measuring range, it is known to use characteristic fields for the precontrol and associated adapted characteristic fields (U.S. Pat. No. 4,676,215). However, processes necessary for this involve very complex calculations, for which reason they are not feasible in the foreseeable future with the microcomputers usual in motor vehicle electronics.
The same also applies to precontrolling and feedback controlling a controlled variable on devices other than an internal combustion engine. The influencing variable need not necessarily be the air flow, it may, for example, also be the viscosity of the fluid to be delivered by a pump or the ventilation of the space to be kept at a certain temperature or any desired disturbance. The calibration need not necessarily be performed with the control-manipulated value maintained at 0, but this is of particular advantage since then use of the control is minimized in operation.
The invention is based on the object of specifying a method for precontrolling and feedback controlling a controlled variable, which compensates for effects caused by aging for each range by influencing the precontrolled variable. The invention is also based on the object of specifying an apparatus for carrying out such a method.